Method of manufacturing a hollow elongated thin-walled metallic body

ABSTRACT

A HALLOW, ELONGATED, THIN-WALLED BODY IS FORMED BY WELDING AT LEAST ONE SEAM TO CLOSE THE BODY AROUND A MANDREL OF A MATERIAL HAVING A GREATER COEFFICIENT OF THERMAL EXPANSION THAN THE MATERIAL OF THE BODY, WHEREAFTER THE BODY AND MANDREL ARE HEATED UNTIL THE THERMAL STRESSES IN THE BODY ARE GREATER THAN THE YIELD STRENGTH OF THE MATERIAL OF THE BODY. THE MANDREL HAS PROJECTING RIDGES RUNNING LONGITUDINALLY AT ITS CORNERS, AND LONGITUDINAL GROOVE IN WHICH IS MOUNTED A SUPPORT MEMBER WHICH UNDERLIES THE SEAM. THE BODY IS THEN PASSES BETWEEN ROLLERS TO FINISH THE SEAM.

Feb. 2, 1971 s, BRANDBERG ETAL 3,559,278

METHOD OF MANUFACTURING A HOLLOW ELONGATED THIN-WALLED METALLIC BODY ,Filed June 3, 1968 3 Sheets-Sheet 1 Q l! I I I w r 1 1% ll Ii I AAAAx'xAAAAAAA IN VEN TOR 5' BRANDBERG' 6) -ew STAN GLAMDIN Feb. 2, 1971 5, BRANDBERG ETAL 3,559,278

' v METHOD OF MANUFACTURING A HOLLOW ELONGATED THIN-WALLED METALLIC BODY Filed June '3, 1968 3 Sheets-Sheet 2 INVENTORS SVEN BRAMDBERG- W cm 's'm/v GLANDIU Feb. 2, 1971 s; BR'ANDBERG ETAL 3,559,278

' METHOD OF MANUFACTURING A HOLLOW ELONGATED THIN-WALLED METALLIC BODY Filed June 5. 1968 3 Sheets-Sheet 5 INVENTORS syn-2N l3 RAN DBE arr By QQNQ H A GLA D N United States Patent Oflice 3,559,278 METHOD OF MANUFACTURING A HOLLOW ELONGATED THlN-WALLED METALLIC BODY Sven Brandberg, Irsta, and Constan Glandin, Vasteras, Sweden, assignors to Allmanna Svenska Elektriska Aktiebolaget, Vasteras, Sweden, 21 Swedish corporation Filed June 3, 1968, Ser. No. 734,061 Claims priority, application Sweden, June 6, 1967, 7,889/ 67 Int. Cl. B231: 31/02 US. Cl. 29-487 7 Claims ABSTRACT OF THE DISCLOSURE A hollow, elongated, thin-walled body is formed by welding at least one seam to close the body around a mandrel of a material having a greater coeflicient of thermal expansion than the material of the body, whereafter the body and mandrel are heated until the thermal stresses in the body are greater than the yield strength of the material of the body. The mandrel has projecting ridges running longitudinally at its corners, and a longitudinal groove in which is mounted a support member which underlies the seam. The body is then passed between rollers to finish the seam.

BACKGROUND OF THE INVENTION (1) Field of the invention The present invention relates to a method of manufacturing with minimum deviation from a given'basic dimension a hollow, relatively thin-walled body having at least one cylindrical hole, the length of which is greater than the width. By thin-walled is meant here and in the following that the ratio between the wall-thickness and the width of the hole is less than 0.1, and by cylindrical is meant the geometrical definition.

(2) The prior art In order to be able to manufacture bodies of the abovedescribed type, for example tubes, with minimum deviation from a given basic dimension, it has previously been necessary to manufacture these from solid material by means of various processes, for example, rolling, forging or drawing processes. Tubes manufactured in the above manner are usually called seamless tubes and are comparatively expensive.

Tubes having seams are usually called welded tubes, regardless of how the joint has been effected, and are usually manufactured from tape-shaped material. Previously, however, these tubes have been unable to fulfill the requirements of minimum deviation from a given basic dimension but are less expensive than the seamless tubes.

SUMMARY OF THE INVENTION One object of the invention is, without disregarding the requirement of great accuracy of dimension and with relatively simple equipment to be able to manufacture a hollow, relatively thin-Walled body with at least one cylindrical hole, the length of which is greater than the width. This is possible according to the invention by joining at least two parts to form said body, on a mandrel having minimum deviation from a given basic dimension, manufactured of a material having a greater coefficient of thermal expansion than the section parts, and by subjecting the body fixed on the mandrel to plastic deformation by heating until thermal stresses arising in the body are greater than the yield strength of the material in the body.

The method according to the invention is particularly suitable for manufacturing metal objects which, apart from the above-mentioned characteristic features, have 3,559,278 Patented Feb. 2, 1971 high melting point and low coefficient of thermal expansion. It is also excellent for manufacturing metal tubes, such as sheathing tubes for fuel assemblies in nuclear reactors, particularly sheathing tubes with substantially circular, hexagonal or square cross section.

In order to obtain the desired accuracy of dimension when manufacturing hollow bodies by means of the above-described method, thus, the mandrel must have minimum deviation from a given basic dimension and be manufactured of a material having a greater coefficient of thermal expansion than the parts to be joined to form said hollow body. So that the plastic deformation can be held within a suitable temperature interval, the coefficient of thermal expansion of the mandrel should be at least 1.5 times greater, and preferably equal to or greater than 2-3 times that of the parts. Those skilled in the art will immediately perceive that there are unlimited possibilities of combining suitable materials for the parts and the mandrel. For this reason as an example it is only mentioned that, in the manufacture of sheathing tubes for fuel assemblies of zirconium alloys, it has been suitable to select stabilised stainless steel as the material for the mandrel, having a coeflicient of linear expansion of 12-19 l'0 deg. C.*

Another suitable material for the mandrel is an alloy consisting of 65.3% Fe, 25% Al and 9.7% Cr. This alloy has a constant coefiicient of linear expansion of approximately 40-10- deg. C." from 0 C. to above 1000 C. and the advantages of its use will be indicated in the following.

In the manufacture of tubes the parts consist of structural bars which, with special reference to metal tubes, are joined together preferably by means of welding. For sheathing tubes for fuel assemblies TIG-welding (Tungsten Inert Gas) is preferably used or electron beam welding under vacuum. After joining the parts, the hollow body can be shrunk onto the mandrel by cooling and then inserted in a furnace, preferably a vertical furnace, and heated to a suitable temperature. By suitable temperature is meant the temperature at which the hollow body is plastically deformed by the mandrel to such an extent that the predetermined dimensions are obtained after cooling. For metal tubes this temperature may be stated to be 250-950 C., for sheathing tubes of zirconium alloys suitably 50055=0 C. when a mandrel of stainless steel is used and 250300 C. when a mandrel of the abovementioned iron-aluminium-chromium alloy is used. The use of a material for the mandrel which has a very high coefficient of thermal expansion enables the sheathing tube to be manufactured of cold-worked or tempered zirconium alloys which have a considerably higher yield strength than annealed alloys. This means that the wall thickness in the sheathing tubes can be decreased, with obvious advantages. Examples of the yield strength of zirconium alloys are given in Table I.

By Zr2.5% Nb in Table I is meant a zirconium alloy containing 2.5 percent by weight niobium. The composition of Zircaloy is seen from Table II.

In certain cases it is suitable for the hollow body to be surrounded by a radially supporting casing during the heating period. The value of the coefficient of thermal expansion of the casing should in this case lie between that of the mandrel and that of the hollow body.

The heating takes place under vacuum or in protective gas, for sheathing tubes of zirconium alloys, suitably tube. FIG. 3 shows, partly in vertical section along the line IIIIII in FIG. 2, how the sheathing tube shrunk on the mandrel is passed between the rollers and FIG. 4 shows, partly in vertical section along the line III-III in FIG. 2, a support roller in the rolling equipment.

under high vacuum, that is, lower pressure than torr, or in protective gas of helium or argon, and should be as DESCRIPERRED rapid as possible in order to avoid undesired material and/or structural alternations such as, for example, grain FIG 1 Shows how two Structural bars and are growth. For other materials different protective gases may 10 joined by means of 1 i on a mandrel 2 s l be selected, for example H for W and Mo and N fo FIG. 3 which shows the welded sheathing tube on the some other metals. After a preferably rapid cooling the mandrel 2 The mandrel 2, Which may be 5 long f r hollow body usually detaches itself from the mandrel, or example is f t d with great accuracy and h requires only slight force to be released. However, if dea maximum deviation in straighthess f 0 8 mm d a sired a release gent m y b u d between the mandrel maximum deviation as far as twisting is concerned of 0.1 and the hollow body, for examPle glass PP e mm. The mandrel 2 shown is manufactured of a stabimahufactufiug sheathing tubes for fuel assemblies 3 lized stainless steel having a coetficient of linear expan- Cohhlm alloy having low neutron absorption cross-Sec sion of approximately 16-l0 deg. C.- and is intended tion is selected as material for the tube, for example Zircf the manufacture f Sheathing tubes having Suhstahaloy-4 or Zircaloy,-2, the composition of which is given tially Square cross sectioh in Table when manufacturing Sheathing tubeS haying The mandrel is constructed of a hollow central body Substantially Square cross-Section, two P Channel 3 from which four axially running ridges extend radially, bars are Preferably used four Similar angular Structural said ridges having tapered cross-section and rounded top. bars which are welded together on the mandrel to form a A groove 5 in the mandrel ll l to the id 4 can hlbe- 111 the Same y, hexagonal Cross-Section two, take up a support member which will be described below. three or six similarly shaped angular structural rods are In the shown embodiment two h structural used having Such a Shape that together y Produce the bars 1' and 1" of Zircaloy are welded together to form a desired cross-section. In the usual manner welding seams h hi b 1 In 1 a tungsten electrode, i should be avoided at the corners. Finally, with a circular hated 6 i Surrounded by a nozzle 7 for protective gas, cross-section, two or more structural bars are used havf example argon h nozzle 7 rests h h h strips ing arc-shaped sections. 8 against the jaws 9 which are part of a fixture, not shown The Process is 110 y Suitable manufacturing long in detail, to keep the U-shaped structural bars 1' and 1" hollow bodie 811011 88 tubes, but y of course also be in position against each other. From below the adjacent used for manufacturing hOllOW bOdlCS too short to be edges of the [Lshaped tructural bars are supported by regarded as tubes. In such cases the process is part1cua Support member 10 i th groove 5 i th d l 2 larly Sllltablti in the manufacture of metal hOllOW bodies The upport member 10 has a channel 11 running axially having high melting Point (above 1500 and low under the welding seam. The channel 11 can be supplied efiicient of linear expansion (less than 10- 10* deg C with protective gas and, together with the space 12 formed Examples of such metals are given in Table II below. between the strips 8 and the jaws 9 which contains pro- TABLE II Zircaloy-Z Zircaloy-4 Mo W Ta Nb Melting point 1,850 1,850 2,620 3, 370 2, 996 1, 950 Coeflicient of linear expansion deg. Ow 6-10- 6'10- 4.9-10- 4.3-10- 6.5-10- 7.2-10- 1 The composition of Zircaloy-2 is: Sn 1.31.6%, Fe 0.070.2%, Cr 0.050.15%, Ni 0.03 0.08%, Zr remainder. The composition of Zircaloy-4 is, with the following exceptions, the same as for Zircaloy-Z: Fe OAS-0.24%, N i(is not included as a constituent in the alloy).

Among other things, in order to reduce the number of tective gas, contributes to producing a welding seam of welding seams it may be advantageous to start with a plate, for example a sheet of metal, and bend this to an unjoined hollow body having substantially the desired cross section, and then join the hollow body by a suitable method, for example welding, on the mandrel. This means that instead of at least two parts, only one part is necessary, having two edges adjacent to each other, said edges being joined together, after which the hollow body obtained is subjected to the above-described treatment in order to obtain exact dimensions.

The joint formed by welding is preferably rolled before the heating process and while the hollow body is still on the mandrel.

The method of the present invention is described as being used in connection with a novel type of mandrel, which represents the preferred mode of operating the process which mandrel, however, is the invention of Erik Hellman and is claimed in a separate application.

BRIEF DESCRIPTION OF THE DRAWINGS a vertical view of equipment for simultaneously rolling two oppositely situated welding seams in a sheathing high quality. On both sides of the channel 11 and in the parts of the jaws 9 situated nearest the welding seam, parallel and axial channels 13 are arranged for cooling water. The coolant channels 13 are advantageously designed so that they are in yielding contact with the U- shaped sections 1 and 1" and leakage of the protective gas is thus minimised.

In order to obtain a smooth sheathing tube wall it is suitable to roll the seam formed by welding before the sheathing tube on the mandrel is subjected to heat treatment. FIG. 2 shows a rolling means enabling the two welding seams to be rolled simultaneously.

The sheathing tube 1 surrounds the mandrel and rests on a number of supporting rollers 14 arranged in pairs and made of a suitable plastic material, for example Bakelite. As shown more clearly in FIG. 4, the support rollers 14 are arranged on shafts 15 journalled in columns 16 projecting from the stand 17. At one end of the stand 17 is a holder 18 to which two extended rods 19 are attached. The rods 19 are longer than the sheathing tube 1 and the mandrel 2 and rest in the grooves 5 along the entire welding seam up to two large rollers 21 and 22 arranged one on top of the other in a press stand 20. The press stand 20 is arranged approximately in the middle of the stand 17. The position of the lower roller 22 is permanent while the upper roller 21 is journalled in a slide 23 which is vertically movable against the spring force of the spring 24. The rolling pressure is adjusted by turning the handle 25. Each rod 19 is provided with a pairof small rollers 26 and 27 arranged one above the other on the vertical line between the upper large roller 21 and the lower large roller 22. These small rollers 26 and 27 project a little outside the upper and lower surfaces of the rod 19 so that, when the mandrel 2 and the sheathing tube 1 are pushed forward so that the rolling process can start, the rod 19 will run in the groove 5 without being directly in contact with the bottom of the groove. During the rolling the bottom of the groove 5 may be proected by a plate 28 of tempered tool steel, which material is also suitable for the rollers 21, 22, 26 and 27. As seen in FIG. 3, the rollers 21 and 22 are provided with projecting parts 21 and 22', the width of which corresponds to the width of the rollers 26 and 27.

After rolling, the sheathing tube is ready to be plastically deformed by means of the previously described heat treatment. The straightness of the tube can be even further improved by stretching it after the heat treatment.

It is obvious to one skilled in the art how the means and method described above should be modified to enable the manufacture of sheathing tubes with, for example hexagonal or circular cross-section instead of square cross-section.

What is claimed is:

1. A method of manufacturing welded high-precision tubing for nuclear reactors in which the tube material is an alloy having a low neutron absorption cross section and a coefiicient of linear expansion of at most -10- deg. C7 which comprises applying around an elongate mandrel (2), manufactured with high precision with respect to lateral dimensions, straightness and lack of twisting about its longitudinal axis and manufactured of a metallic material having a high melting point and a coefiicient of linear expansion which is at least 1210- deg. C.- but at least twice the coefficient of linear expansion of the tube material, a split sheet metal tubular body (1', 1") of the tube material having at least one longitudinal slot bounded by two closely fitting edges, welding said edges together by means of longitudinal butt welding to form a tube (1) on the mandrel (2), the tube shrinking on the mandrel because of the cooling of the welding seam, heating the tube and mandrel to such a temperature that the mandrel (2), which expands more than the tube (1), subjects the tube to tangential stress sufficient to create tensile stresses in the tube (1) greater than the yield strength of the tube material, thereby deforming the tube (1) plastically, the heating being continued until the tube 1) after subsequent cooling acquires predetermined lateral dimensions, whereby the tube (1) manufactured by means of welding and plastically deformed by the mandrel (2) has the required degree of accuracy with respect to lateral dimensions, straightness and lack of twisting about its longitudinal axis.

2. Method according to claim 1 for manufacturing sheathing tubes having symmetrical polygonal cross-section, in which the sheet metal body (1', 1") consists of at least two elongate, straight sections of a zirconium alloy having angular cross-section.

3. Method according to claim 2, in which the material of the mandrel is a stabilized stainless steel having a coefiicient of linear expansion of about 16- 10- degf 4. Method according to claim 3, in which the mandrel with the shrunk tube is heated to about 500550 C.

5. Method according to claim 2, in which the material of the mandrel is an alloy containing about 65.3% Fe, 25% Al and 9.7% Cr.

6. Method according to claim 5, in which the mandrel with the shrunk tube is heated to about 25 0300 C.

7. Method according to claim 1, in which after the heat treatment the tube (1) is stretched to improve the straightness.

References Cited UNITED STATES PATENTS 375,043 12/ 1887 Bogert 72364X 1,363,160 12/1920 Murray, Jr., et al 29447 1,586,249 5/1926 Krogh et al 29474.1 1,594,526 8/ 1926 Hume 29473.9X 2,386,747 10/ 1945 Ris. 3,050,613 8/1962 Sheinhartz 29447X 3,140,108 7/1964 Klein et al. 29504X 3,141,227 7/ 1964 Klepfer et al. 29504X 3,372,467 3/1968 Crowdes l. 29473.9X 3,384,946 5/ 1968 Ward, Jr 29497.5X

JOHN F. CAMPBELL, Primary Examiner R. I. SHORE, Assistant Examiner US. Cl. X.R. 

